stunthanger.com

Building Tips and technical articles. => 1/2 A building. => Topic started by: Larry Renger on October 23, 2009, 03:32:21 PM

Title: New model underway - Sky Streak 250
Post by: Larry Renger on October 23, 2009, 03:32:21 PM

I have upped the size and revised the look of my forward swept design, so renamed it the Sky Streak 250.  It will be powered by the AP Wasp .061 and features trike gear.  It will use a balloon tank.  I have flown the last, Black Widow powered, version in competition and trophied with it, so I have great expectations for this "killer" version.

Note a couple of things.  First that the wing construction is self-jigging, being built on equal height blocks pinned to the horizontal stiffeners.  Second, those little square marks on the fuselage are 1/8" sticks that go through all the parts to assure perfect registration.

Title: Re: New model underway - Sky Streak 250
Post by: kenneth cook on October 24, 2009, 06:55:14 AM

        Larry , out of curiousity I was wondering why the cross bridging on the spars. At least this is what we call it in carpenters terms. I typically see vertical grain shear webbing in that application. Is that just a design choice? Ken

Title: Re: New model underway - Sky Streak 250
Post by: don Burke on October 24, 2009, 10:48:31 AM

I'll answer that one.

The diagonals do the same thing as a shear web.  A web makes the rectangle formed by the rib and spars into a plane more resistant to deforming.  The diagonals turn the rectangle into a triangle which is also resistant to deforming.  The weight of a strip or a thin web are about the same, but the strips are for me easier to install and do take less glue.  Besides that they look a lot "cooler" with transparent covering!

Title: Re: New model underway - Sky Streak 250
Post by: Larry Renger on October 24, 2009, 09:56:38 PM

Don is correct except that the cross webbing is stronger than pure shear web.  Look at any old iron briges.  They used links, not webs.  The grain aligns the strongest direction of the wood where it is needed.

Also, it is lighter an easier to fit in, and if you look closely, one link is ahead of the spar, the other is behind, forming a nice box structure with minimum weight.  Clearly it is way lighter than carrying the sheeting out farther, and reduces the stress concentration at the end of the sheeting.

The only reason not to carry it out farther is pure lazyness!

Title: Re: New model underway - Sky Streak 250
Post by: Larry Renger on October 30, 2009, 10:22:43 AM

More progress.  New photos.

Title: Re: New model underway - Sky Streak 250
Post by: minnesotamodeler on October 30, 2009, 03:10:43 PM

My brother had a Super Clown with wings just like that...right after he flew it into a tree trunk.

Title: Re: New model underway - Sky Streak 250
Post by: john e. holliday on October 31, 2009, 09:10:56 AM

Boy that looks wicked.  Have fun,  DOC Holliday

Title: Re: New model underway - Sky Streak 250
Post by: Larry Renger on November 03, 2009, 10:08:11 PM

More progress!  The framework is complete, no sanding on the tips or cheek cowls (tank containing box).  All up weight is 3.5 ounces!  This puppy will weigh in under 7 when complete, I think.  And that with a 250 sq.in. wing.  WORLD BEWARE!!!   VD~

Title: Re: New model underway - Sky Streak 250
Post by: Robert McHam on November 04, 2009, 01:41:03 AM

Models like this mean a lot to me as I have always felt that even a slight forward sweep could be very advantageous. Keep it up Larry.

Robert